1. Field of the Invention
The invention relates to image patterning techniques and more particularly to subtractive imaging techniques, which are defect insensitive and highly repeatable.
2. Background Description
Traditional optical lithography has been used for years to image and pattern silicon during the fabrication of semiconductor devices. As the size of semiconductor devices decreases, traditional optical lithography becomes limited for patterning purposes due to the wave-length size of the electromagnetic radiation used to image the pattern. For example, by reducing the pitch of the images, the contrast is also reduced. Additionally, resolution achievable by the imaging radiation is directly proportional to the imaging radiation's wavelength.
Also, optical lithography techniques have been aggressively pushed to print features with dimensions having smaller and smaller fractions of the printing wavelength. This, in turn, results in smaller and smaller process windows, expensive use of assist features with questionable benefit and extendability, as well as linewidth control, particularly at gate definition, which consumes larger portions of device tolerances. This is unacceptable from a design standpoint. It is thus becoming increasingly more difficult to achieve projected performance and density projections.
One illustration clearly shows these problems. At gate level, lithography targets must be almost twice the desired final image size, necessitating dry-etch image size shrinking (“trims”) to shrink the images. The trims are nesting-sensitive and pattern-sensitive adding further to a lack of tolerance control.
Because imaging size will ultimately be limited by the inherent limitations of the imaging radiation in lithographic techniques, other techniques to pattern a semiconductor device have been developed. For example, sidewall image transfer (“SIT”) techniques have been developed, which is an edge printing process using the edges of a mask for imaging purposes. Accordingly, SIT methods allow a reduction in size of patterns without a size limitation imposed by imaging radiation.
However, current SIT methods suffer from pattern density issues and are known to magnify defects because the materials used in SIT imaging will coat all sides of debris on the surface to be imaged thereby magnifying the size of the debris. Additionally, current SIT methods can have poor control and thus make it difficult to image small objects with repeatable dimensions.